Nozzle size change does not affect machine settings

[ThomasHH 0]

Cura by default includes G-code for two start lines to prime the nozzle before printing begins. The settings for these start lines are part of the start script G-code for the printer and are therefore unaffected by any changes made in the regular "print settings".

I recently upgraded from a 0.4mm nozzle to a Volcano setup with a 0.8mm nozzle and initially experienced that my extruder could not force filament through the nozzle when I started a print - even though I had just loaded filament and watched it ooze from the nozzle. Turns out the problem was that even though I had updated the print settings to produce 0.6mm layers etc, Cura's start script still dictated the printer to move the head to 0.28mm distance from the bed for the first two lines (standard settings for a 0.4mm nozzle).

The immediate fix was to correct the printing height in the start script G-code, but my question is: Cura allows you to define a custom nozzle size but since a printer only has one set of "machine setting", the option to change nozzle is in my case potentially damaging to the printer, as e.g. printing height can be (and was) ignored. Is there any way to have separate machine settings for each nozzle size? and e.g. have the two print lines be defined in the print settings along with everything else? - Otherwise thanks for a great piece of software!

 

 

Thanks in advance

[gr5 2,230]

I'm going to give you a partial answer.  Hopefully someone else can give you a better answer.  So every cura setting has a variable that can be inserted into the start g-code script.  Including initial layer height.  So you can do something like this:

 

G1 X0.1 Y20 Z{initial_layer_height}

(I think that works exactly as is - all lower case with underscores but I'm not 100% certain)

 

So that solves your issue of hitting the glass.  however you need to adjust the extruder amount - otherwise it's only going to extrude enough for a 0.3 high, 0.4 wide bead of filament.  To do that you need to multiply:

{initial_layer_height}*{initial_layer_line_width}*1.2345   where 1.2345 is a constant depending on filament diameter and length of line printed. I just pulled that number out of thin air as I'm lazy

 

HOWEVER, you can't do math in these (or can you?  90% sure you can't.  @GregValiant what you think of all this?).  So I don't know how you would do that.

 

A good compromise would be to leave the layer height alone, and double the extrusion amount.  A 0.4mm nozzle can print a 0.8mm line usually just fine.  Especially at these extra low printing speeds.  And then even if you had a 1.2mm nozzle you should get enough filament to come out to hopefully stick to the glass.

 

Another solution is to have multiple "printers" each with a fixed nozzle size and you switch between "machines" in Cura when you switch nozzles.

 

This is not an issue for Ultimaker printers because they don't do a purge line (I really like the idea of purge lines by the way).  I wish purge line was a feature in Cura instead of hidden in start g-code.

 

So that's another solution: get rid of purge lines and stick with purging in the corner in mid-air followed by a retraction.  I mean the skirt/brim option takes care of the purge line concept for he most part.

[GregValiant 1,351]

#1.  Cura by default provides no purge lines at all.  The purge lines come from the printer definition file that was developed by a third party at the behest of the printer manufacturer (a small percentage may have been written by members of the Cura community).  Either way, the definition files were then submitted to Ultimaker for inclusion in Cura.  In the case of Creality printers, "Trouch.Com" was the author of the printer definition files for all models of the Creality printers.  Ultimaker includes them (thank you) but it would be silly to expect Ultimaker to buy one of every model printer on the planet so they could check the machine definitions.  It would be just as silly to try to support a third party printer with a fourth part hot end that was installed by a fifth party.  BUT, there are ways.

 

You could just put semi-colons in front of the purge lines.  The printer would ignore them and the skirt or brim would be your purge lines.

 

You could add a second printer identical to the one you have but with start Gcode configured for the big nozzle.  One of the lines from my Creality start gcode is:

G1 X0.1 Y200 Z0.3 E15

That E value of 15 is not a calculation, but rather just a number somebody pulled out of their... ear.  If calculated it would be 9.  I assume the heavy flow is because it is only a purge line whose only purpose is to get the plastic flowing.

Going to a .8 nozzle at .6 layer height and an extrusion 180mm long using 1.75 filament would just require:

G1 X0.1 Y200 Z{layer_height_0} E36

In this case I did calculate the E as (extrusion_length / ((area_of_filament_cross_section) / (layer_height * line_width)).  The "layer_height_0" in curly brackets gets replaced with the real number when Cura generates the gcode.

 

Having the second printer configured in Cura is the easiest thing to do.  Pick the printer, pick your "0.8 Nozzle" settings profile and you're good to go.